you have narrowed down on the possibilities ; methinks - f4 and iso 3200 should work indoors and give very usable shots. Try to keep shutter speed around 1.5 times focal length - if you have a reasonably steady hand that should do. And for Auto focus settings change from release priority to focus priority - that will prevent you from clicking away while the camera is still un-focussed. I got myself a D800 about 6 months back - the camera really challenges you to be perfect - its not to be used/treated like a point and shoot. Give it some respect and practice and the results can be astounding !